Autism spectrum disorder (ASD) affects 1:68 children in the United States. There is now a consensus that multiple genetic loci combined with exposure(s) to unidentified environmental risk factors during neurodevelopment influence ASD susceptibility and symptom severity. Epidemiological studies consistently implicate traffic-related air pollution as an ASD risk factor, with the strongest associations found late in the gestational period and in early life. There is a paucity of research on the developmental neurotoxicity of air pollutant exposures in preclinical animal models, and to date, there are no reports testing the hypothesis that inhaled traffic-related pollution impairs behavior relevant to the ASD phenotype. Moreover, whether or not inflammatory consequences from vehicular emissions are related to ASD pathology is unknown. The objectives of this proposal are to analyze effects of exposure to traffic-related air pollution on ASD-relevant phenotypes. We hypothesize that exposure of the developing brain to toxic inhaled pollutants will cause neuroinflammation and interfere with normal patterns of neuronal connectivity and result in phenotypes associated with ASD. We further hypothesize that these histological and behavioral deficits will be exacerbated by one gene strongly implicated in ASD, ProSAP2/Shank3. To test this hypothesis, we will use an innovative exposure model that delivers real-time air samples from the Caldecott tunnel, near San Francisco. Polluted tunnel air will be delivered to subjects housed adjacent to the tunnel while control animals will be exposed to filtered air. We will also use a novel transgenic rat model of disrupted Shank3 expression. SHANK3 mutations are among the more prevalent and reliably replicated monogenic causes of ASD. These studies will clarify the role of driving on, living near, and attending schools adjacent to busy roadways in the onset and/or severity of ASD-relevant phenotypes. This project will leverage the NIH-funded MIND Institute Intellectual and Developmental Disabilities Research Center (IDDRC), of which the PI and Co-Investigator are members, to support the histological analyses and behavioral studies. These studies are needed to corroborate human studies linking developmental exposures to traffic-related air pollution to increased risk for ASD. The confirmation of traffic-related air pollution as an environmental risk factor for ASD will provide a rationale for controlling exposures to traffic-related air pollution during critical periods of neurodevelopment thereby reducing the incidence of ASD and/or decreasing the severity of symptoms. This proposal will develop a gene-environment approach that could be expanded to investigate other autism risk genes in future grant proposals.